Showing papers in "Physiologia Plantarum in 1975"

Enzymes of heavy-metal-resistant and non-resistant populations of Silene cucubalus and their interaction with some heavy metals in vitro and in vivo

Abstract: The in vitro and in vivo effects of copper, zinc, cadmium, nickel, cobalt, and manganese on nitrate reductase, malate dehydro-genase, isocitrate dehydrogenase, and glucose-6-phosphate dehydrogenase of zinc-, copper- and non-resistant populations of Silene cucubalus were investigated. During the in vitro experiments no resistant enzyme could be detected; enzymes of resistant and non-resistant ecotypes had a similar sensibility to all the metals. Nitrate reductase was the most sensitive enzyme. During the in vivo experiments remarkable differences were found. The nitrate reductase and the isocitrate dehydrogenase of the zinc-resistant population were activated when adding zinc to the culture medium, especially the nitrate reductase showed high activities at zinc concentrations where the nitrate reductase of the non-zinc-resistant populations was nearly completely inhibited. The zinc-resistant ecotype had a real need for zinc.

Effects of Activated Charcoal on Growth and Morphogenesis in Cell Cultures

Abstract: The effects of activated charcoal on growth and morphogenesis in plate cultures of different plant cells have been studied. It was shown that medium containing charcoal induced embryogenesis in cultures of Daucus carota in which embryo formation could not be brought about by omitting auxin from the medium. Charcoal-medium also induced abundant root formation in older cultures of Allium cepa, which normally did not produce roots. The growth of cultures of Glycine max and Haplopappus gracilis was totally inhibited by charcoal. It is thought that activated charcoal removes substances from the medium, one of which might be auxin.

Radial Oxygen Loss from Roots: The Theoretical Basis for the Manipulation of Flux Data Obtained by the Cylindrical Platinum Electrode Technique

Abstract: A resume is given of the cylindrical platinum electrode technique for measuring the rate of oxygen release from the submerged roots of intact plants. Methods are then described for manipulating the oxygen flux data to quantify the following root characteristics: total effective internal diffusional resistance, non-metabolic (pore-space) resistance, internal apical oxygen concentration, effective diffusion coefficient of internal transport and fractional porosity, and the respiratory contribution to internal transport. The diffusional resistance of the root wall is discussed and the method formerly suggested for converting low temperature flux data to the appropriate room temperature values (Armstrong 1971) is revised. Finally, suggestions are made for overcoming the difficulties encountered in using flux data for comparative work if the roots differ in their apical radii.

Respiration and Vitality of Binucleate and Trinucleate Pollen

Abstract: The respiration and vitality of ungerminated bi- and trinucleate pollen were studied in order to determine the influence of relative humidity and temperature on metabolic activity The gas exchange, germination capacity and staining with tetrazolium bromide were followed under standardized conditions A constant respiration rate occurred under conditions of high relative humidity (97%) Per mg pollen, the trinucleate grains of Compositae and Gramineae respired 2 to 3 times as intense as 6 species of binucleate grains Per unit of pollen protein the differences were even larger In contrast to binucleate pollen, the longevity of trinucleate pollen was very short and the ability to germinate was lost twice as fast as the respiration capacity This limits the use of tetrazolium bromide as an indicator of viability At reduced relative humidities respiration was strongly restricted, but the longevity of bi- and trinucleate pollen considerably increased Pollen of Gramineae, however, was very sensitive to changes in relative humidity; short exposure to low relative humidity decreased both the vitality and the capacity to respire

Germination of Seeds in the Shadow of Plants

Abstract: An attempt to prove the ecological significance of red-far red control mechanisms in seed germination was made. The seeds of 30 species were exposed beneath the plant canopies. All the normally light-stimulated seeds, and also seeds of 14 (out of 19) “insensitive’ species and seeds of 1 (out of 4) light-inhibited species, were inhibited or significantly retarded in their germination, as compared with seeds exposed to diffuse light in an artificial construction. Further experiments with “insensitive’ seeds of Lactuca sativa L. cv. Cud Vorburgu showed that after prolonged plant-shadow treatment the seeds became light-sensitive in the usual phytochrome-mediated manner. Seeds exposed under the plant canopies during a few days were extremely sensitive to red or white light, but this sensitivity diminished slowly in the course of treatment. The spectral composition of light filtered through the leaves shows great preponderance of far red radiation. The red-far red reversion can be simply obtained with the natural light and a leaf. In open stands bright weather retards considerably the germination of lettuce, cloudy weather brings about full germination. Some considerations on the ecological significance of seed behaviour, particularly as connected with plant competition, are given.

Phase Change in Hedera helix: Induction of the Mature to Juvenile Phase Change by Gibberellin A3

Abstract: A sensitive and reproducible method to obtain GA3 induced morphological reversion of mature Hedera helix to the juvenile form has been developed Dose response experiments indicate that GA3 stimulates reversion over a 50–100 fold range with a half maximal response at approximately 05 μg GA3 per plant The individual characteristics involved in phase change revert to the juvenile form in a sequential manner as GA3 dose is increased Variations in light intensity from 12–36 × 104 lux and temperature from 15 to 26°C do not affect this hormonal response Other growth regulators including indoleacetic acid, kinetin, abscisic acid and (2-chloroethyl)phosphonic acid (Ethephon) are inactive but other gibberellins (GA1 and a mixture of A4–A7) are active in stimulating reversion Therefore, the response is specific for gibberellins as a class of hormones but non-specific for a particular form of gibberellin The significance of this response in relation to juvenility in woody plants is discussed

The effect of IAA on sugar accumulation and basipetal transport of 14C-labelled assimilates in relation to root formation in Phaseolus vulgaris cuttings

Abstract: The effect of indol-3yl-acetic acid on root formation, accumulation of 80% ethanol-soluble sugars and basipetal transport of 14C-labelled assimilates has been investigated in Phaseolus vulgaris (cv. Canadian Wonder) hypocotyl cuttings. The removal of leaves reduced root formation in the hypocotyl, while excision of the apical bud was less detrimental. The expression of the IAA effect in inducing more roots was dependent on the area of leaves, and was found to be better when all leaves were present. Sugars accumulated slowly at the base of cuttings during a four-day period after excision, and IAA greatly enhanced this accumulation. By comparing sugar content at the base of green and starved cuttings it was established that IAA greatly increased it concurrently with root formation. IAA applied in solution to the hypocotyl greatly enhanced the basipetal transport of 14C-labelled assimilates and their accumulation at the hypocotyl during a 24-h period. The IAA-induced accumulation was found to be connected with a greater mobilization of labelled assimilates from upper parts of the cutting. Experiments involving pretreatment with IAA and transport in cuttings already possessing root primordia, suggest a dual effect of IAA: (I) a direct effect on transport, and (2) an increase in the root-“sink”. It is concluded that both may be operating in inducing basipetal accumulation of labelled assimilates. It is suggested that one of the roles of IAA in promoting rooting of cuttings is to increase sugar availability at the site of root formation.

Endogenous shoot growth rhythms and indeterminate shoot growth in oak

Abstract: Wide variations of shoot growth patterns in saplings of pin oak (Quercus palustris Muenchh.) have been observed as a consequence of varying environmental conditions, experimental manipulations, and vigor of trees. Shoot growth patterns range from a series of recurrent, determinate flushes, constituting a genuine endogenous rhythm, to continuous, indeterminate growth. Observed growth patterns agree well with those predicted by a model of rhythmic growth which assumes the dependence of shoot growth on the functional equilibrium between shoot and root system. Indirect evidence suggests that cessation of shoot growth under favorable environmental conditions might be a consequence of internal water deficits. Observed differences in shoot growth patterns between young and mature trees are discussed as logical consequences of the model.

Effect of Salinity and Potassium on the Uptake of Nitrogen and on Nitrogen Metabolism in Young Barley Plants

Abstract: In a solution culture experiment with 4-week-old barley plants (variety Villa) the influence of NaCl salinization and of KCl additions on the uptake and turnover of labelled N (15NH415NO3) was studied. Labelled N was applied for 24 h at the end of the growth period. Salinization impaired growth and uptake of labelled N. The incorporation of labelled N into the protein fraction, however, was improved by NaCl salinization. Additions of KCl to the nutrient solution diminished the negative effect of NaCl salinization on growth. At both NaCl salinization levels (60 and 120 mM) K additions favoured the uptake of labelled N and particularly its incorporation into the protein fraction. It is suggested that the negative influence of the NaCl stress is not primarily due to an impaired protein synthesis, but is possibly caused by a deterimental effect of Na on other metabolic processes.

Freeze Preservation of Cultured Plant Cells

Abstract: A slow rate of cooling (1–2°C/min) is essential for high survival during the freezing phace. Death of cells during this phase takes place at temperatures below the freezing point of the suspending media, predominantly in the temperature range 10°C to −50°C. In the absence of cryoprotectants survival drops to zero between −30°C and −40°C. Fast thawing (water bath at 37°C giving a rate of temperature rise of 120°C/min between −50°C and −10°C) yields the highest recovery of viable cells. An interaction between cooling rate and thawing rate was demonstrated; this served to emphasize the importance of fast thawing. Under the best conditions realized in these experiments the percentage survival of cells cooled to −196°C was for carrot 70–75%, for belladonna 30–40% and for sycamore 20–25%. Storage for long periods (up to 10 months) at −196°C did not lead to any decline in percentage survival. Carrot cultures which had been stored for 10 months at −196°C showed no change in cell morphology or growth potential in culture and retained embryogenic potential.

Phenolic Content in Male and Female Carica papaya: A Possible Physiological Marker for Sex Identification of Vegetative Seedlings

Abstract: The phenolic composition was determined in the leaves, petioles and bark tissues of male and female plants of two papaya cultivars. The same kind of phenolics were isolated from the male and female plants. However, a marked difference was observed between the plant organs of different cultivars. The important free and bound phenolics extracted after acidic and alkaline hydrolysis were caffeic acid, gentisic acid, m-coumaric acid, p-coumaric acid, salicylic acid and quercetin. Four phenolic compounds were not identified. The amounts of free, acid-hydrolysable and alkali-hydrolysable phenolic compounds were considerably higher in male plants.

Volatilization of Mercury by Algae

Abstract: The presence of Chlorella cells in a medium containing HgCl2 causes a rapid decrease of the mercury content in the algal suspension. The rate of decrease depends on the inoculum concentration. The presence of Hg in the medium induces a lag in the growth, whose length depends on the initial concentration of Hg and of the inoculum. Binding and/or uptake of mercury by the cells is not dependent on temperature. The mercury content per cell declines somewhat at the time at which the culture resumes growth at a rate similar to that of the controls without mercury.

Acidification of the Medium Associated with Normal and Fusicoccin-Induced Seed Germination

Abstract: Fusicoccin, a toxin stimulating cell enlargement and inducing proton extrusion in various plant tissues, has been shown to replace kinetin, gibberellic acid and red light in breaking seed dormancy. It also removes the inhibitory effect of abscisic acid. The present data also show that the stimulating effect of fucicoccin on embryo growth of decoated radish (Raphanus sativus L.) and maize (Zea mays) seeds and on the development of maize embryos is accompanied by an early, significant acidification of the medium. Acidification of the medium is also observed when fusicoccin reverses the abscisic acid-induced inhibition of germination. These results support the hypothesis that the mode of action of fusicoccin in promoting germination involves, as in stimulation of cell enlargement, the activation at the cell membrane level of proton extrusion processes. The physiological significance of fusicoccin-induced release of protons at the onset of germination is discussed in comparison with the results concerning the mechanism of action of fusicoccin on cell enlargement in other plant materials.

Changes in Endogenous Plant Hormones in Cherry Tomato Fruits during Development and Maturation

Abstract: Hormonal extracts of cherry tomato fruits (Lycopersicon esculentum Mill.) cv. Small Fry at different stages of fruit development and maturation were bioassayed for their auxin, gibberellin, cytokinin and growth inhibitor activities. In general, the levels of endogenous growth promoters were much higher in the young developing fruits than in the more mature fruits. Free cytokinin levels were highest in the first two weeks of development then declined rapidly. However, cytokinin activity in the ribotide fraction, after treatment with alkaline phosphatase, decreased during thefirst three weeks of development then increased rapidly over the following four weeks. Auxin levels increased during early development to reach a maximum in three-week-old fruits after anthesis. Gibberellin levels during the first two weeks of development were much lower than those of auxins and cytokinins, but then increased to reach a peak in the fourth week after anthesis. A growth inhibiting substance with Rf similar to that of abscisic acid was found in the acidic fraction of the fruit extracts. This inhibitor increased gradually during fruit growth and development and reached a peak at the age of five weeks which coincides with the green mature stage.

The Role of Cellulase and Polygalacturonase in Abscission of Young and Mature Shamouti Orange Fruits

Abstract: During the first eight weeks after setting young citrus fruits gradually lose their ability to abscise at the abscission zone between the stem and the pedicel; in fruits older than eight weeks abscission occurs at the calyx area. The activity of cellulase and polygalacturonase in the two abscission zones was markedly increased before and during abscission, and was localized mainly in the abscission zone. Ethylene accelerated the increase in enzymic activity after an 8- to 10-h lag period; 2,4-D delayed abscission and enzymic activity when applied during the first 24 h after excision. During this period 2,4-D also partly suppressed the enhancing effect of ethylene. Early application of cyclo-heximide inhibited the formation of the enzymes and thus abscission was delayed to a certain extent. Although there are some indications that the relationship between enzymic activity and abscission is a complex one, the data presented indicate that cellulase and polygalacturonase play a significant role in abscission of citrus fruits at various developmental stages. Both enzymes act almost simultaneously and are equally controlled by ethylene and 2,4-D.

Regulation of Water Loss by Citrus Leaves

Abstract: The factors responsible for the low transpiration rates of citrus were investigated. Leaf resistance to water vapor exchange by orange seedlings (Citrus sinensis L. cv. Koethen) including a substantial boundary layer resistance, was as low as 1 s cm−1 in humid air. Leaf resistance of well watered plants increased to values as large as 5 s cm−1 when the difference in absolute humidity between leaf and air was increased. Leaf resistance was only slightly influenced by temperature between 20 and 30°C providing the humidity difference between leaf and air was kept constant. Leaf resistance increased when leaf temperature was increased between 20 and 30°C when the absolute humidity external to the leaf was kept constant. Increased humidity differences resulted in greater increases in leaf resistance during initial experiments than when the experiments were repeated with the same leaves indicating acclimation by the plant. It was concluded that the effects of humidity differences on leaf resistance are partially responsible for the low transpiration rates of citrus.

An Evaluation of Some Parameters Required for the Enzymatic Isolation of Cells and Protoplasts with CO2 Fixation Capacity from C3 and C4 Grasses

Abstract: Variable factors affecting the enzymatic isolation of mesophyll protoplasts from Triticum aestivum (wheat), a C3 gras, and mesophyll protoplasts and bundle sheath strands from Digitaria sanguinalis (crabgrass), a C4 grass, have been examined with respect to yields and also photosynthetic capacity after isolation. Preparations with high yields and high photosynthetic capacity were obtained when small transverse leaf segments were incubated in enzyme medium in the light at 30°C, without mechanical shaking and without prior vacuum infiltration. Best results were obtained with an enzyme medium that included 0.5 M sorbitol, 1 mM MgCl2, 1 mM KH2PO4, 2% cellulase and 0.1% pectinase at pH 5.5. In gerneral, leaf age and leaf segment size were important factors, with highest yields and photosynthetic capacities obtained from young leaves cut into segments less than 0.8 mm. To facilitate the cutting of such small segments, a mechanical leaf cutter is described that uniformly (± 0.05 mm) cuts leaf tissue into transverse segments of variable size (0.4–2 mm). Isolations that required more than roughly 4 h gave poor yields with reduced photosynthetic capacity; however, using the optimum conditions described, functional preparations could be roughly 2 h. High rates of light dependent CO2 fixation by the C4 mesophyll protoplasts required the addition of pyruvate and low levels of oxalacetate, while isolated bundle sheath strands and C3 mesophyll protoplasts supported CO2 fixation without added substrates. Rates of CO2 fixation by isolated wheat protoplasts generally exceeded the reported rates of whole leaf photosynthesis. Wheat mesophyll protoplasts and crabgrass bundle sheath strands were stable when stored at 4°C while C4 mesophyll protoplasts were stable when stored at 25°C.

Influence of N‐Deficiency on the Abscisic Acid Content of Sunflower Plants

Abstract: Sunflower plants (7 weeks old) were transferred from a modified Hoagland solution to a N-free nutrient medium and kept there for 7 days. Abscisic acid (ABA) was determined in several parts of the plants and in exudates collected from the roots of some of these plants. N-deficiency considerably increased the ABA content of the leaves, especially the older ones, and also considerably increased the ABA content of the upper parts of the stem when compared to the control plants. In the roots and the exudates of these plants no ABA could be detected. After dissecting the stems the ABA content in the roots of the control plants with normal N supply dropped quickly, probably due to rapid metabolization. Judging by results obtained, it seems unlikely that the roots are responsible for the remarkable increase of the ABA content in the shoots caused by N-deficiency.

Growth Regulators and the Phytochrome-Mediated Dormancy of Celery Seeds

Abstract: Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA4 and GA7 (GA4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N′-4-pyridylurea (NC5392) with GA4/7 were observed. Varietal differences in response to GA4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA4/7 or cytokinin in addition to low GA4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N6-benzyladenine but not by GA4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.

Identification of Zeatin and Zeatinriboside in Coconut Milk

Abstract: Zeatin and zeatinriboside were identified from the milk of mature Cocos nucifera fruits. It would appear as if the two compounds are present in roughly equal proportions. Ethyl acetate extraction in a liquid-liquid extractor at an alkaline pH (8.0) proved to be a very efficient method of extracting zeatinriboside. Partitioning with water-saturated n-butanol proved to be the best way of extracting zeatin.

Effects of SO2 on Photosynthesis and Nitrogen Fixation

Abstract: Responses of photosynthesis and nitrogen fixation to NaHSO3 (10−5−5 × 10−3M) were investigated in the lichen Stereocaulon paschale (L.) Fr. and the blue-green alga Anabaena cylindrica Lemmermann. The treatments were performed in buffered media with varying pH (5.8–8.1) and light conditions (0–32 W × m−2). The activities of the intact organisms were investigated, under the same environmental conditions, with 14C liquid scintillation and acetylene reduction techniques respectively. The nitrogen fixation proved to be more susceptible than photosynthesis, in both organisms, and in all cases treatments at pH 5.8 were more inhibitory than at higher pH-values. Treatment with 5 × 10−4M NaHSO3 at pH 5.8 caused no reduction of photosynthesis in S. paschale, while the inhibition of nitrogen fixation was 97%. For A. cylindrica the corresponding values were 40% and 75% respectively. Short-time treatments of A. cylindrica showed that the nitrogen fixation was more rapidly affected than photosynthesis. The inhibition of nitrogenase activity and CO2-fixation was smaller in the dark and increased at higher light intensities. Both processes showed a good capacity for recovery after removal of the NaHSO3 solution. Also the clumping ability of A. cylindrica was disturbed by NaHSO3 treatments.

Uptake of Zinc and Strontium by Brown Algae

Abstract: The accumulation of radioactively labelled strontium and zinc by living and killed tips of the brown alga Ascophyllum nodosum (L.) Le Jol. was studied and compared with the uptake in some model substances. The accumulation of strontium was reversible, and similar in living and killed plants. Equilibrium was established within a couple of days. Strontium accumulation seemed to be an ionexchange process involving the negatively charged intercellular polysaccharides, probably mainly alginate. Only a small fraction of the zinc uptake in living algae seemed to be due to a similar ion exchange with the intercellular polysaccharides. The characteristic features of the zinc uptake was a constant, slow, irreversible accumulation persisting for very long periods of time. In dead algae the uptake was rapid and reversible, indicating that the algae contained zinc-binding substances which were not directly accessible to the zinc ions in the surrounding seawater before killing. It is proposed that these substances in the living plant are contained in membrane-surrounded structures, probably vacuoles. These membranes, effectively regulating the zinc uptake in the living cells, are destroyed by killing, making the zinc binding substances directly accessible. The transfer of zinc from the reversible intercellular sites to the irreversible cellular sites continued undisturbed during low-tide periods. The intercellular charged polysaccharides thus function as ion buffers, allowing ion uptake into the cell at a constant rate, independent of the tidal movements.

Inhibition of Corn and Sunflower Photosynthesis by Lead

Abstract: Detached corn and sunflower leaves supplied with PbCl2 via the transpiration stream exhibited reduced rates of photosynthesis. The difference between species in the amount of Pb taken up was in direct proportion to their respective transpiration rates. For both species the reduction in photosynthesis and the amount of Pb taken up increased with increasing treatment concentrations. A corresponding reduction occurred in the rate of transpiration suggesting that stomatal resistance may be increased by Pb contamination. The pathways of CO2 and water vapor exchange are discussed in relation to the effects of Pb on photosynthesis and transpiration.

Activity Changes in Selected Enzymes from Soybean Leaves Following Ozone Exposure

Abstract: Soybeans [Glycine max(L.) Merr.] were harvested at various time periods after a 2-h exposure to either 0 or 0.5 μ1/1 ozone to determine the effects of ozone on selected enzymes. Carbohydrate metabolism was modified by a depression of glyceraldehyde 3-phaosphate dehydrogenase and an activation of glucose 6-phosphate dehydrogenase. Ozone did not alter the levels of RNase, protease, acid phosphatase or esterase as might be expected if ozone enhanced leaf senescence. The activities of phenylalanine ammonia lyase, polyphenol oxidase and peroxidase were initially depressed and then stimulated following the ozone exposure. The reactions of soybeans to an acute ozone stress were more nearly akin to those elicited in response to other stresses than to the process of senescence.

Effects of light on the georeaction and growth inhibitor content of roots

Abstract: The positive geotropic response of the apical segments prepared from the primary roots of Zea mays depends upon at least one growth inhibitor, produced by the root cap, moving basipetally into the extending zone of the root in which it accumulates in the lower part. Anjou maize reacts in both darkness and light while Kelvedon maize is, for the first few hours, geotropic only in light. The production (or activity) of the growth-inhibiting substance — tested by using vertical half-decapitated root segments — is quite similar to the georeaction. This finding provides strong evidence that, in the case of Kelvedon maize roots, the inhibitory substance may depend on light. Observations related to the root segment of Anjou and Kelvedon maizes of which the tips are exchanged, are in agreement with the above results.

Peroxidases as indicators of growth and differentiation in Aspen callus cultures

Abstract: Aspen (Populus tremuloides Michx.) callus tissue grown on a synthetic medium containing either an auxin (2,4-dichloro-phenoxyacetic acid) or cytokinin [6-(3-methyl-2-butenylamino) purine] differed in growth rate, total peroxidase activity, peroxidase isoenzyme expression, and in lignin, cell wall sugars and extractive content. Tissue treated with auxin increased more rapidly in fresh weight, but stopped growing sooner than did the cytokinin-treated tissues. Lignification also proceeded more rapidly, and lignin formed a greater fraction of the cell wall weight in auxin-treated tissue. For both treatments, peroxidase activity and growth rate were positively related (r = 0.96). Polyacrylamide gel electrophoresis showed some quantitative, but few qualitative, isoenzyme differences with hormonal treatment and growth rate.

Effect of Indoleacetic Acid on the Abscisic Acid Level in Stem Tissue

Abstract: Excised stem sections from growing plants of Populus tremula L. and Pisum sativum L. including lateral buds were treated with indole-3-acetic acid in a phosphate buffer solution. In control sections the level of the abscisic acid-like inhibitor decreased strongly during 24 h as did the level of the endogenous auxin. Exogenous indoleacetic acid counteracted the decrease in the inhibitor level to a considerable extent. Implications of this auxin effect in relation to apical dominance are discussed.

Properties of Extracellular Enzymes from Aphanomyces astaci and Their Relevance in the Penetration Process of Crayfish Cuticle

Abstract: In culture filtrates from the crayfish plague parasite, Aphanomyces astaci, protease and a low level of hyaluronidase activity were found. The hyaluronidase activity was highest at pH 6.5 or above and at about 23°C. The protease activity had a broad pH-optimum, between pH 7 and at least pH 10, and was partially denatured at 30°C. However, when incubated for 30 min with the substrate, casein, the activity increased logarithmically up to about 35–40°C and had an apparent optimum at 45–50°C. The proteases from the parasitic as well as from two less proteolytic, saprophytic Aphanomyces species were predominantly constitutive and were excreted mainly by the older mycelia. Proteases from the parasite and a saprophyte did not reach full activity until 10–30 min after substrate addition. No lipase activity was found in the case of the mycelium of the parasitic species. However, esterase was apparently present inside germinating zoospores. The native enzymes of A. astaci could degrade freeze-dried soft cuticle from crayfish. The relevance of the different enzymes of A. astaci for the penetration process within the cuticle of crayfish is discussed.

Evidence for Three Different Systems of Movement of Indoleacetic Acid in Intact Roots of Phaseolus coccineus

Abstract: Indoleacetic acid (IAA)-5-3H (2 × 10−9M) was applied to intact roots of Phaseolus coccineus seedlings, at the apex or 2 cm above the apex, at various pHs and in the presence of Cu2+ and NaCl. The transport of label in the roots was then examined after 6 h by cutting the roots into 1 mm sections above and below the zone of treatment. Basipetal movement from 2 cm above the apex was unafected by pH, Cu2+ or NaCl. Acropetal movement from the same area decreased with increasing pH from 5.4 to 8.0, probably due to an effect of pH on the entry of IAA into the cells. pH had no effect on sucrose transport. Cu2+ also inhibited acropetal movement but NaCl had no effect. Basipetal movement of label from the apex was reduced by Cu2+ and increasing pH, but not as much as with acropetal movement, and increased by the presence of NaCl. These facts are interpreted as showing 3 different systems of IAA movement in intact roots: basipetal from 2 cm up the root in some extracellular physical system; acropetal from 2 cm up the root, and basipetal from the apex, in a metabolically dependent intracellular system, but in different tissues of the root. It is proposed that endogenous IAA not only moves into the root from the stem but is also synthesized in the root apex, and moves basipetally for a short distance to the root growing zone in a separate system from the IAA descending from the stem.